1. Field of the Invention
The present invention relates to a linear compressor and more particularly to a moving magnet type of linear compressor that is of a high efficiency and used for a cooling machine. The present invention is concerned with an improved linear compressor so constructed as to ensure that the linear compressor effectively increases a density of magnetic flux passing through an electromagnet unit to impart an increased thrust force to a piston forming part of the linear compressor.
2. Description of the Related Art
There have so far been proposed a wide variety of prior-art linear compressors one of which is exemplified and shown in FIG. 8. The prior-art linear compressor 10 thus proposed comprises a fixed member 11 formed with a hermetically sealed compression chamber to receive a working fluid therein, a piston rod 12 slidably movably supported by the fixed member 11 and connected to the piston serving to compress the working fluid in the compression chamber, a magnet unit 13 including a plurality of yoke portions 14 and 15 accommodated in the piston rod 12 and a permanent magnet 16 in the form of a rectangular shape in cross-section and supported by the yoke portions 14 and 15 to be positioned in the center portion of the piston rod 12 and an electromagnetic unit 17 including a peripheral portion 18, a plurality of yoke portions 19 and 20 radially inwardly extending from the peripheral portion 18 and a plurality of magnetic coils 21 and 22 each wound around each of the yoke portions 19 and 20. The permanent magnet 16 of the magnet unit 13 is arranged in face-to-face relationship with the yoke portions 19 and 20 of the electromagnet units 17 in the longitudinal direction of the piston rod 12.
The prior-art linear compressor thus constructed encounters such a problem as failing to effectively increase the density of magnetic flux passing through the yoke portions 19 and 20 of the electromagnet units 17 by the reason that the permanent magnet 16 of the magnet unit 13 is embedded in the center portion of the piston rod 12 as shown in FIG. 8. The failure in effective increase of the density of magnetic flux makes it almost impossible to impart an increased thrust force to the piston forming part of the linear compressor.
It is therefore a primary object of the present invention to provide a linear compressor that can effectively increase the density of magnetic flux passing through the electromagnet unit to impart an increased thrust force to the piston forming part of the linear compressor.
It is another object of the present invention to provide a linear compressor that can increase the operating efficiency.
It is a further object of the present invention to provide a linear compressor that can be reduced in size.
It is a still further object of the present invention to provide a linear compressor that can reduce the electric consumption.
It is a yet still further object of the present invention to provide a linear compressor that can reduce the electric heat value.
In accordance with a first aspect of the present invention, there is provided a linear compressor, comprising: a retaining member; a fixed member supported by the retaining member and formed with a hermetically sealed compression chamber to receive a working fluid therein, the fixed member having a longitudinally central portion formed with a inlet-outlet port having the working fluid introduced therein and discharged therefrom; a pair of pistons axially movably received in the compression chamber to assume respective compression positions where the working fluid is compressed in and discharged out of the compression chamber through the inlet-outlet port and respective retraction positions where the working fluid is expanded and introduced in the compression chamber through the inlet-outlet port; a pair of piston rods each having an outer peripheral portion and slidably movably supported by the fixed member, the piston rods respectively connected to the pistons to have the pistons axially move in the compression chamber, each of the piston rods made of a ferromagnetic material; a plurality of magnet units mounted on each of the outer peripheral portions of the piston rods, each of the magnet units having a plurality of magnet segments each made of a permanent magnet and circumferentially arranged with neighboring two magnet segments different in magnetic pole; a plurality of electromagnet units supported by the retaining member to be axially spaced apart from each other in predetermined relationship with the magnet units, respectively; and resilient means for resiliently urging the piston rods to cause the piston rods to assume respective neutral positions between the compression positions and the retraction positions.
Each of the electromagnet units may include a peripheral portion, a plurality of yoke portions radially inwardly extending from the peripheral portion and integrally formed with the peripheral portion, the yoke portions being circumferentially equally spaced apart from each other, and a plurality of magnetic coils each wound around each of the yoke portions.
Each of the yoke portions of electromagnet units may have an axial length substantially equal to that of each of the magnet units.
The magnet units may include neighboring two magnet units having respective center planes each perpendicular to the center axis of each of the piston rods, and the yoke portions of the electromagnet units have respective center planes each perpendicular to the center axis of each of the piston rods, each of the center planes of the yoke portions of the electromagnet units being positioned between the center planes of the neighboring two magnet units when the piston rods assume their respective neutral positions.
Each of the yoke portions of the electromagnet units may be constituted by a plurality of piled plates each made of a ferromagnetic material and having a plane extending along the center axis of each of the piston rods.
The linear compressor may further comprise a pair of positioning members each mounted on the fixed member with respect to the magnet units, each of the positioning members formed with a plurality of annular grooves axially spaced apart from each other, each of the annular grooves functioning to facilitate positioning of each of the yoke portions of the electromagnet units with the magnet units.
Each of the yoke portions of the electromagnet units may have a radially outer end portion made of a ferromagnetic material and a radially inner end portion made of a ferromagnetic material having a saturated density of magnetic flux higher than that of the ferromagnetic material of each of the radially outer end portions of the yoke portions to ensure that the density of magnetic flux of each of the yoke portions of the electromagnet units is more increased than that of each of the yoke portions of the electromagnet units which are made of the same ferromagnetic materials.
The ferromagnetic material of each of the radially inner end portions may be made of Permendur.
Each of the magnet segments of the magnet units may be constituted by a plurality of piled plates each made of a permanent magnet and having a plane extending perpendicular to the center axis of each of the piston rods.
The resilient means may include a plurality of resilient members disposed along each of the piston rods, each of the resilient members constituted by a plurality of leaf springs each having a plane extending perpendicular to the center axis of each of the piston rods, each of the resilient members having a inner end portion fixedly connected to each of the piston rods and a outer end portion fixedly connected to the fixed member to ensure that each of the piston rods is resiliently urged and restored to the respective neutral positions when each of the piston rods is axially moved to the compression positions and the retraction positions.
The fixed member may have an inner peripheral portion held in sliding engagement with the pistons and made of a material substantially equal in thermal expansion coefficient to the material of each of the pistons.
The pair of pistons and the pair of piston rods may be located in symmetrical relationship with each other with respect to the inlet-outlet port.
The resilient members may be located in symmetrical relationship with each other with respect to the inlet-outlet port.
The working fluid may be made of a gas selected from the group consisting of helium, nitrogen, hydrogen, and neon-argon.
The permanent magnet of each of the magnet segments may be made of a ferroalloy containing nickel.
In accordance with a second aspect of the present invention, there is provided a linear compressor, comprising: a retaining member, a fixed member supported by the retaining member and formed with a hermetically sealed compression chamber to receive a working fluid therein, the fixed member having a longitudinally end portion formed with a inlet-outlet port having the working fluid introduced therein and discharged therefrom; a piston axially movably received in the compression chamber to assume a compression position where the working fluid is compressed in and discharged out of the compression chamber through the inlet-outlet port and a retraction position where the working fluid is expanded and introduced in the compression chamber through the inlet-outlet port; a piston rod having an outerperipheral portion and slidably movably supported by the fixed member, the piston rod connected to the piston to have the piston axially move in the compression chamber, the piston rod made of a ferromagnetic material; a plurality of magnet units mounted on the outer peripheral portion of the piston rod, each of the magnet units having a plurality of magnet segments each made of a permanent magnet and circumferentially arranged with neighboring two magnet segments different in magnetic pole; a plurality of electromagnet units supported by the retaining member to be axially spaced apart from each other in predetermined relationship with the magnet units, respectively; and resilient means for resiliently urging the piston rod to cause the piston rod to assume neutral position between the compression position and the retraction position.
Each of the electromagnet units may include a peripheral portion, a plurality of yoke portions radially inwardly extending from the peripheral portion and integrally formed with the peripheral portion, the yoke portions being circumferentially equally spaced apart from each other, and a plurality of magnetic coils each wound around each of the yoke portions.
Each of the yoke portions of electromagnet units may have an axial length substantially equal to that of each of the magnet units.
The magnet units may include neighboring two magnet units having respective center planes each perpendicular to the center axis of the piston rod, and the yoke portions of the electromagnet units have respective center planes each perpendicular to the center axis of the piston rod, each of the center planes of the yoke portions of the electromagnet units being positioned between the center planes of the neighboring two magnet units when the piston rod assumes its neutral position.
Each of the yoke portions of the electromagnet units may be constituted by a plurality of piled plates each made of a ferromagnetic material and having a plane extending along the center axis of the piston rod.
The linear compressor may further comprise a positioning member mounted on the fixed member with respect to the magnet units, the positioning member formed with a plurality of annular grooves axially spaced apart from each other, each of the annular grooves functioning to facilitate positioning of each of the yoke portions of the electromagnet units with the magnet units.
Each of the yoke portions of the electromagnet units may have a radially outer end portion made of a ferromagnetic material and a radially inner end portion made of a ferromagnetic material having a saturated density of magnetic flux higher than that of the ferromagnetic material of each of the radially outer end portions of the yoke portions to ensure that the density of magnetic flux of each of the yoke portions of the electromagnet units is more increased than that of each of the yoke portions of the electromagnet units which are made of the same ferromagnetic materials.
The ferromagnetic material of each of the radially inner end portions may be made of Permendur.
Each of the magnet segments of the magnet units may be constituted by a plurality of piled plates each made of a permanent magnet and having a plane extending perpendicular to the center axis of the piston rod.
The resilient means may include a plurality of resilient members disposed along the piston rod, each of the resilient members constituted by a plurality of leaf springs each having a plane extending perpendicular to the center axis of the piston rod, each of the resilient members having a inner end portion fixedly connected to the piston rod and a outer end portion fixedly connected to the fixed member to ensure that the piston rod is resiliently urged and restored to the neutral position when the piston rod is axially moved to the compression position and the retraction position.
The fixed member may have an inner peripheral portion held in sliding engagement with the piston and made of a material substantially equal in thermal expansion coefficient to the material of the piston.
The working fluid may be made of a gas selected from the group consisting of helium, nitrogen, hydrogen, and neon-argon.
The permanent magnet of each of the magnet segments may be made of a ferroalloy containing nickel.